Here in Tucson, AZ the local belief seems to be that there is no need for antifreeze (although three consecutive nights of 18° in January of 2012 and a late freeze this year did wake up some folks), and water is a better coolant than anything else, so why dilute the water (or more likely, pay for more than water)? Corrosion protection is rarely if ever given a thought and bright orange coolant due to iron oxide is considered normal.
As a result, I have never seen or heard of a greater number of freeze-cracked blocks and heads nor of a greater number of rusted through (from the inside) blocks and heads as exists here due to this local superstition. "Rust free" maybe a popular description of the exterior of cars from the southwest but "heart failure" may be a more honest description of the water-cooled passages of many engines here. Soluble oil as a rust-preventative ought to be called "gullible-oil" if we had real truth in advertising.
In my opinion, there is no better corrosion protection (for the dollar) than that provided by 50:50 antifreeze:water (ethylene glycol or propylene glycol). If you are contemplating using a "corrosion preventative" for the summer to paper over a summer overheating problem, than I would recommend fixing the real problem, your inadequate radiator.
An alternative maybe waterless coolants (no water, no corrosion) which are typically an expensive blend of ethylene glycol and propylene glycol (with proprietary buffers and corrosion inhibitors) however I am unaware of any info regarding their coolant efficiency and use in non-pressurized systems.
I would be happy to contemplate empirical data for the long-term superiority of non-glycol based corrosion preventatives (cost and effect) because I want to preserve my property and a piece of history but all I have ever seen are anecdotes and advertising, not data derived using the scientific method. I am not from Missouri but I am a scientist, so show me.